The present invention relates generally to devices for supporting and driving an open-end spinning rotor and, more particularly, to a rotor supporting and driving assembly having a shaft with a free end in the form of a support rod made of a material harder than steel and disposed in engagement with a ball of an axial bearing, sometime referred to as an axial bearing, within a receptacle concentric to the shaft axis.
In open-end spinning devices, the speed of the spinning rotors is conventionally above 100,000 rpms. Such high speeds place significant requirements on the support of the rotors. German Patent Publication DE 25 14 734 teaches a support arrangement for an open-end spinning rotor which is still used even for the highest speeds of a spinning rotor previously attained.
The rotor cup itself in which the yarn is formed is supported on an elongated shaft which rests on two support-disk pairs set slightly obliquely relative to one another with the free end of the shaft supported on a ball in the axial direction. This achieves a low-wear support. The ball functions as a contact for the rotor shaft and is placed in vibration via a holder for the ball. As a result, the ball is held at support points which are constantly changing. The support-disk pairs for the shaft support are placed slightly obliquely relative to each other to exert a component of force on the shaft to repeatedly urge the shaft and the rotor in the direction of the ball and to return the shaft into contact with the ball whenever the shaft end is lifted off the ball. The position of the ball relative to the axial centerline of the rotor shaft is constantly changing. A minimal eccentricity between the shaft axis and the center of the ball brings about a driving of the ball so that the ball constantly presents a new contact point to the end face of the free shaft end. During the oscillating axial motion of the rotor shaft, wear occurs to the ball and on the shaft end during the rapid succession of the lifting off of the shaft end from the ball and its falling back onto the ball. In particular, if the shaft end is shortened due to deformation or removal of material, an error in the yarn count [i.e. the size of the yarn being spun] can occur because of changes caused in the position of the rotor relative to the yam infeed.
In order to minimize the wear of the shaft end, U.S. Pat. No. 5,349,809 teaches the insertion of a ceramic pin as a so-called axial engagement element on the free end of the shaft in a concentric receptacle of its offset end piece. A front side of the ceramic pin is supported on the ball of the axial bearing. The pin is inserted with very close manufacturing tolerances into the receptacle. Since the receptacle is a blind hole the air in the blind hole must be offered a possibility of escape during the insertion of the pin. This is provided in the state of the art by an enlargement of the blind hole to receive the compressed air or by grooves extending in the longitudinal direction of the pin distributed over its circumference to offer the escaping air a pathway for exiting the receptacle.
These known possibilities have several disadvantages. A notching of the pin on its circumferential surface by the ventilation grooves leads to a reduction of the contact pressure between the pin and the receptacle and thereby reduces the effectiveness of the adhesion of the pin in the shaft. In the case of sharp-edged transitions of the grooves to the circumferential surface of the shaft there is the danger that, when the pin is inserted into the blind hole, material chips off on account of unfavorable variations in stress, which damages the pin. If the pin does not have any ventilation grooves the blind hole must be longer that the pin. Preventive measures must then be taken so that the pin can not shift in the blind hole under load.